It is well known to use limited slip differentials to detect differences in rotational speed between two shafts containing braking discs arranged to rotate with each of the two shafts, and to be engaged when a certain difference in rotational speed is reached. In order to activate the engagement of the braking discs, a detection device is required to detect the difference in rotational speed, and to mechanically engage the braking discs. In previous arrangements, the detection device has been complicated and has exhibited functional problems.